Golf ball

ABSTRACT

Disclosed is a golf ball having a cover formed from a thermoplastic polyurethane material which can be recycled for molding, which exhibits high restitution, and which exhibits excellent scuff resistance and discoloration resistance. The cover is formed from a composition (C) containing, as predominant components, the following components (A) and (B):  
     (A) a polyurethane material mixture of a thermoplastic polyurethane material (a-1) and dicyclohexyl-4,4′-methane diisocyanate (a-2), and  
     (B) an isocyanate mixture in which an isocyanate compound (b-1) having at least two isocyanate groups serving as functional groups in the molecule is dispersed in a thermoplastic resin (b-2) which is substantially non-reactive with the isocyanate groups.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a golf ball having a coverformed from a thermoplastic polyurethane material; and more particularlyto a golf ball having a cover formed from a thermoplastic polyurethanematerial which can be recycled for molding, which exhibits highrestitution, and which exhibits excellent scuff resistance.

[0003] 2. Description of the Related Art

[0004] In recent years, polyurethane materials have become of interestas materials for forming a golf ball cover. Polyurethane materials areclassified into thermosetting polyurethane materials and thermoplasticpolyurethane materials, and a process for forming a thermosettingpolyurethane material into a product differs from a process for forminga thermoplastic polyurethane material into a product. A thermosettingpolyurethane material can be formed into a product through the followingprocedure: a urethane prepolymer having an isocyanate end group and acuring agent such as polyol or polyamine, which serve as liquid rawmaterials, are mixed under heating; and the resultant mixture is feddirectly to a mold and then heated, to thereby allow urethane curingreaction to proceed.

[0005] Many studies have heretofore focused on golf balls formed fromthermosetting polyurethane materials. For example, U.S. Pat. Nos.5,334,673, 6,117,024, and 6,190,268 disclose such golf balls. Meanwhile,U.S. Pat. Nos. 5,006,297, 5,733,428, 5,888,437, 5,897,884, and 5,947,843disclose forming methods of thermosetting polyurethane materials.

[0006] Since a thermosetting polyurethane material exhibits nothermoplasticity, the material and a product formed from the materialcannot be recycled. In addition, when a thermosetting polyurethanematerial is employed for forming a specific product such as a golf ballcover (i.e., a product which covers a core), efficient production of theproduct is not attained, since the heating-curing step and the coolingstep of the material requires long time, and high reactivity andinstability of the material make control of the molding time verydifficult.

[0007] In the case where a thermoplastic polyurethane material is formedinto a molded product, the product is not directly obtained throughreaction of raw materials, but is formed from a linear polyurethanematerial—an intermediate—which has been synthesized by employment of rawmaterials and a synthesis method, the raw materials and the methoddiffering from those employed in the case of the aforementionedthermosetting polyurethane material. Such a linear polyurethane materialexhibits thermoplasticity, and is cured through cooling. Therefore, sucha polyurethane material can be molded by use of an injection moldingmachine. Injection molding of a thermoplastic polyurethane material is atechnique suitable for forming a golf ball cover, since the molding timeof a thermoplastic polyurethane material is much shorter than that of athermosetting polyurethane material, and a thermoplastic polyurethanematerial is suitable for precise molding. Meanwhile, a thermoplasticpolyurethane material can be recycled, and is thus environmentallyfriendly. U.S. Pat. Nos. 3,395,109, 4,248,432, and 4,442,282 disclosegolf balls formed from thermoplastic polyurethane materials.

[0008] However, when a golf ball cover is formed from a conventionalthermoplastic polyurethane material, the resultant golf ball is notsatisfactory in terms of feeling on impact, controllability,restitution, and scuff resistance upon being hit with an iron.

[0009] In order to solve such a problem, Japanese Patent ApplicationLaid-Open (kokai) No. 9-271538 discloses a golf ball cover formed from athermoplastic polyurethane material exhibiting high restitution.However, the disclosed golf ball cover is not satisfactory in terms ofscuff resistance upon being hit with an iron.

[0010] Japanese Patent Application Laid-Open (kokai) No. 11-178949discloses a golf ball cover exhibiting relatively excellent scuffresistance upon being hit with an iron, which predominantly contains areaction product formed from a thermoplastic polyurethane material andan isocyanate compound. When the cover is formed, an isocyanate compoundsuch as a diisocyanate or a block isocyanate dimer, serving as anadditive, is added to a thermoplastic polyurethane material in thecourse of heating, melting, and mixing by use of an extruder, or in thecourse of injection molding, to thereby allow reaction to proceed.

[0011] However, in the case of molding of the cover disclosed inJapanese Patent Application Laid-Open (kokai) No. 11-178949, since anisocyanate compound must be handled with great care due to itsinactivation by moisture, obtaining a stable reaction product isdifficult. Meanwhile, a block isocyanate exhibiting moisture resistanceis not suitable for forming the cover, since a blocking agent issues astrong odor when the isocyanate is thermally dissociated. When anisocyanate compound assumes the form of powder or solution, control ofthe amount of the compound which is added to a thermoplasticpolyurethane material is difficult, and therefore cover propertiescannot be controlled adequately. In addition, since the thermoplasticpolyurethane material differs in melting point and melt viscosity fromthe isocyanate compound, thorough and satisfactory kneading thereof mayfail to be attained in a molding apparatus. Therefore, in the techniquedisclosed in the above publication, the effect of moisture on a covermaterial and the amount of an additive is not satisfactorily controlled,resulting in failure to produce a golf ball cover which is satisfactoryin terms of improvement of scuff resistance.

[0012] Japanese Patent Application Laid-Open (kokai) No. 11-178949discloses an aliphatic isocyanate-based thermoplastic polyurethanematerial to be used as a desirable thermoplastic polyurethane material.However, since the thermoplastic polyurethane material is highlyreactive with isocyanate and its reaction is difficult to control, thepolyurethane material involves the following problems: gelation easilyoccurs before injection molding, and sufficient plasticity cannot bemaintained; gelation may occur during molding of a cover; and thepolyurethane material cannot be recycled, due to gelation. Because ofsuch problems, the thermoplastic polyurethane material is difficult touse in practice.

[0013] Japanese Patent Publication (kokoku) No. 58-2063 (U.S. Pat. No.4,347,338) discloses a process for producing a thermosettingpolyurethane product, in which a compound having two or more isocyanategroups is mixed with a thermoplastic resin which is non-reactive with anisocyanate group, the resultant mixture is incorporated into athermoplastic polyurethane material, and the resultant material issubjected to molding by use of a molding machine. However, the purposeof the technique disclosed in the above publication is to improve thepolyurethane product only in terms of solvent resistance and durabilityagainst continuous, repeating friction, and the publication does notdisclose use of the aforementioned forming material as a material of agolf ball cover. There still exists demand for a golf ball covermaterial which can provide a golf ball with various necessaryproperties, such as restitution, total distance, spin performance,controllability, feeling on impact, scuff resistance, cut resistance,and discoloration resistance.

SUMMARY OF THE INVENTION

[0014] In view of the foregoing, an object of the present invention isto provide a golf ball having a cover formed from a thermoplasticpolyurethane material which can be recycled for molding, which exhibitshigh restitution, and which exhibits excellent scuff resistance anddiscoloration resistance.

[0015] In order to achieve the above object, the present inventionprovides the following golf balls.

[0016] (1) A golf ball comprising a core and a cover therefor, whereinthe cover is formed from a composition (C) containing, as predominantcomponents, the following components (A) and (B):

[0017] (A) a polyurethane material mixture of a thermoplasticpolyurethane material (a-1) and dicyclohexyl-4,4′-methane diisocyanate(a-2), and

[0018] (B) an isocyanate mixture in which an isocyanate compound (b-1)having at least two isocyanate groups serving as functional groups inthe molecule is dispersed in a thermoplastic resin (b-2) which issubstantially non-reactive with the isocyanate groups.

[0019] (2) A golf ball according to (1), wherein the thermoplasticpolyurethane material (a-1) is synthesized from a polyether polyol andan aromatic diisocyanate.

[0020] (3) A golf ball according to any one of (2), wherein thepolyether polyol is a polytetramethylene glycol having an averagemolecular weight of at least 2,000.

[0021] (4) A golf ball according to (2) or (3), wherein the aromaticdiisocyanate is 4,4′-diphenylmethane diisocyanate.

[0022] (5) A golf ball according to any one of (1) through (4), wherein,in the polyurethane material mixture (A), the ratio by weight of thethermoplastic polyurethane material (a-1) to dicyclohexyl-4,4′-methanediisocyanate (a-2) is 100:0.5 to 100:5.

[0023] (6) A golf ball according to any one of (1) through (5), whereinthe isocyanate compound (b-1) in the isocyanate mixture (B) is4,4′-diphenylmethane diisocyanate.

[0024] (7) A golf ball according to any one of (1) through (6), whereinthe thermoplastic resin (b-2) in the isocyanate mixture (B) is athermoplastic polyester resin.

[0025] (8) A golf ball according to any one of (1) through (7) wherein,in the isocyanate mixture (B), the ratio by weight of the thermoplasticresin (b-2) to the isocyanate compound (b-1) is 100:5 to 100:100.

[0026] (9) A golf ball according to any one of (1) through (8), wherein,in the composition (C), the ratio by weight of the thermoplasticpolyurethane material (A) to the isocyanate mixture (B) is 100:1 to100:40.

[0027] (10) A golf ball according to any one of (1) through (9), whereinthe material of the cover has a surface hardness of 40 to 80 as measuredby use of a D-type durometer, and a restitution elastic modulus of atleast 45%.

[0028] (11) A golf ball according to any one of (1) through (10),wherein the material of the cover can be recycled for molding.

DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

[0029] The present invention will next be described in more detail.Firstly, components (A) and (B) and composition (C) will be described.

[0030] (A) Polyurethane Material Mixture

[0031] (a-1) Thermoplastic Polyurethane Material

[0032] The thermoplastic polyurethane material includes soft segmentsformed of a polymeric polyol (polymeric glycol), a chain extenderconstituting hard segments, and a diisocyanate. No particular limitationis imposed on the polymeric polyol serving as a raw material, and thepolymeric polyol may be any one selected from polymeric polyols whichare conventionally employed in the technical field related tothermoplastic polyurethane materials. Examples of the polymeric polyolinclude polyester polyols and polyether polyols. Of these, polyetherpolyols are more preferred to polyester polyols, since a thermoplasticpolyurethane material having high restitution elastic modulus andexhibiting excellent low-temperature properties can be synthesized.Examples of the polyether polyols include polytetramethylene glycol andpolypropylene glycol. From the viewpoints of restitution elastic modulusand low-temperature properties, polytetramethylene glycol isparticularly preferred. The average molecular weight of the polymericpolyol is preferably 1,000 to 5,000. The average molecular weight ismore preferably 2,000 to 4,000, in order to synthesize a thermoplasticpolyurethane material having high restitution elastic modulus.

[0033] Any chain extender which is conventionally employed in thetechnical field related to thermoplastic polyurethane materials ispreferably used. Examples of the chain extender include, but are notlimited to, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol,1,6-hexanediol, and 2,2-dimethyl-1,3-propanediol. The average molecularweight of the chain extender is preferably 20 to 15,000.

[0034] Any diisocyanate which is conventionally employed in thetechnical field related to thermoplastic polyurethane materials ispreferably used. Examples of the diisocyanate include, but are notlimited to, aromatic diisocyanates such as 4,4′-diphenylmethanediisocyanate, 2,4-toluene diisocyanate, and 2,6-toluene diisocyanate;and aliphatic diisocyanates such as hexamethylene diisocyanate. Somediisocyanates involve difficulty in controlling cross-linking reactionduring injection molding. In the present invention, 4,4′-diphenylmethanediisocyanate, which is an aromatic diisocyanate, is most preferred, inconsideration of stability in reaction with the below-describedisocyanate mixture (B).

[0035] In the present invention, a thermoplastic polyurethane materialsynthesized from a polyether polyol and an aromatic diisocyanate is mostpreferred; the polyether polyol is polytetramethylene glycol having anaverage molecular weight of at least 2,000, and the aromaticdiisocyanate is 4,4′-diphenylmethane diisocyanate.

[0036] Preferred examples of the thermoplastic polyurethane materialcontaining the aforementioned materials include commercially availablepolyurethane materials, such as Pandex T-8290, T-8295, and T-8260(products of DIC Bayer Polymer Ltd.), and Resamine 2593 and 2597(products of Dainichiseika Color & Chemicals Mfg. Co., Ltd.).

[0037] (a-2) Dicyclohexyl-4,4′-Methane Diisocyanate (Hydrogenated MDI)

[0038] The purpose of addition of dicyclohexyl-4,4′-methane diisocyanate(a-2) to the thermoplastic polyurethane material (a-1) is to impart across-linking structure to the thermoplastic polyurethane material, andto enhance the strength of the thermoplastic polyurethane material, tothereby reduce the amount of the isocyanate mixture (B) to be added tothe cover material. When the isocyanate mixture (B) is added to thecover material in a large amount, the cover material is considerablydiscolored. However, when dicyclohexyl-4,4′-methane diisocyanate (a-2)to the thermoplastic polyurethane material (a-1) in advance, if theamount of the isocyanate mixture (B) is reduced, the cover materialexhibits scuff resistance similar to the case where the amount of theisocyanate mixture (B) is not reduced, and discoloration of the covermaterial can be prevented.

[0039] In the polyurethane material mixture (A), the ratio by weight ofthe thermoplastic polyurethane material (a-1) todicyclohexyl-4,4′-methane diisocyanate (a-2) is preferably 100:0.5 to100:5, more preferably 100:1 to 100:4. When the ratio ofdicyclohexyl-4,4′-methane diisocyanate (a-2) to the thermoplasticpolyurethane material (a-1) is excessively low, scuff resistanceimproving effect becomes unsatisfactory, whereas when the ratio ofdicyclohexyl-4,4′-methane diisocyanate (a-2) to the thermoplasticpolyurethane material (a-1) is excessively high, viscosity of thepolyurethane material mixture (A) increases due to gelation, resultingin poor moldability.

[0040] (B) Isocyanate Mixture

[0041] The isocyanate mixture (B) is obtained by dispersing theisocyanate compound (b-1) having at least two isocyanate groups servingas functional groups in the molecule in the thermoplastic resin (b-2)which is substantially non-reactive with the isocyanate groups. Theaforementioned isocyanate compound (b-1) is preferably an isocyanatecompound which is conventionally employed in the technical field relatedto thermoplastic polyurethane materials. Examples of the isocyanatecompound include, but are not limited to, aromatic diisocyanates such as4,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, and2,6-toluene diisocyanate; and aliphatic diisocyanates such ashexamethylene diisocyanate. Of these, 4,4′-diphenylmethane diisocyanateis most preferred, in consideration of reactivity and operationalsafety.

[0042] The aforementioned thermoplastic resin (b-2) is preferably aresin having low water-absorbability and high compatibility with thethermoplastic polyurethane material. Examples of the resin includepolystyrene resins, polyvinyl chloride resins, ABS resins, polycarbonateresins, and polyester elastomers (e.g., polyether-ester block copolymersand polyester-ester block copolymers). Of these, in consideration ofrestitution elasticity and strength, polyester elastomers, inter alia,polyether-ester block copolymers, are particularly preferred.

[0043] In the isocyanate mixture (B), the ratio by weight of thethermoplastic resin (b-2) to the isocyanate compound (b-1) is preferably100:5 to 100:100, more preferably 100:10 to 100:40. When the ratio ofthe isocyanate compound (b-1) to the thermoplastic resin (b-2) isexcessively low, a large amount of the isocyanate mixture (B) must beadded to the thermoplastic polyurethane material (A), in order toachieve a successful cross-linking reaction between the isocyanatecompound (b-1) and the thermoplastic polyurethane material (A). As aresult, the thermoplastic resin (b-2) greatly affects the thermoplasticpolyurethane material (A), resulting in unsatisfactory properties of thecomposition (C). In contrast, when the ratio of the isocyanate compound(b-1) to the thermoplastic resin (b-2) is excessively high, thorough andsatisfactory kneading of the isocyanate compound (b-1) into thethermoplastic resin (b-2) is not attained, and thus preparation of theisocyanate mixture (B) becomes difficult.

[0044] The isocyanate mixture (B) can be obtained through, for example,the following procedure: the isocyanate compound (b-1) is incorporatedinto the thermoplastic resin (b-2), and the resultant mixture iscompletely kneaded by use of a mixing roll or a banbury mixer at 130 to250° C., followed by pelletization or pulverization after cooling.Preferred examples of the isocyanate mixture (B) include commerciallyavailable isocyanate mixtures such as Crossnate EM30 (product ofDainichiseika Color & Chemicals Mfg. Co., Ltd.).

[0045] (C) Composition

[0046] The composition (C) comprises, as predominant components, apolyurethane material mixture (A) and a isocyanate mixture (B). In thecomposition (C), the ratio by weight of the thermoplastic polyurethanematerial (A) to the isocyanate mixture (B) is preferably 100:1 to100:100, more preferably 100:5 to 100:50, much more preferably 100:10 to100:30. When the ratio of the isocyanate mixture (B) to thethermoplastic polyurethane material (A) is excessively low, theisocyanate mixture (B) exerts insufficient cross-linking effect, whereaswhen the ratio is excessively high, unreacted isocyanate imparts a colorto the resultant composition.

[0047] In the present invention, the cover-forming material may containother components in addition to the aforementioned components. Examplesof such “other components” include thermoplastic polymer materials otherthan the thermoplastic polyurethane material, such as polyesterelastomer, polyamide elastomer, ionomer resin, styrene block elastomer,polyethylene, and nylon resin. In this case, the incorporation amount ofthermoplastic polymer materials other than the thermoplasticpolyurethane material is 0 to 100 parts by weight, preferably 10 to 75parts by weight, more preferably 10 to 50 parts by weight, on the basisof 100 parts by weight of the thermoplastic polyurethane material whichserves as an essential component. The incorporation amount isappropriately determined in accordance with various purposes, includingregulation of the hardness of the cover-forming material and improvementof the restitution, fluidity, and adhesion of the cover-formingmaterial. If desired, the cover-forming material may further containvarious additives, such as pigments, dispersants, antioxidants,light-resistant stabilizers, UV absorbers, and release agents.

[0048] A cover of the golf ball of the present invention can be formedthrough, for example, the following procedure: isocyanate mixture (B) isadded to polyurethane material mixture (A) and then dry-mixed, and acover is formed from the resultant mixture around a core by use of aninjection molding apparatus. The molding temperature varies with thetype of the thermoplastic polyurethane material (a-i), but is typically150 to 250° C.

[0049] In the resultant golf ball cover, reaction or cross-linking isthought to proceed as follows: an isocyanate group is reacted with aresidual OH group of the thermoplastic polyurethane material, to therebyform a urethane bond; or an isocyanate group is added to a urethanegroup of the thermoplastic polyurethane material, to thereby form anallophanate or biuret cross-linking structure. In this case, althoughcross-linking proceeds insufficiently immediately after injectionmolding of the cover-forming material, cross-linking proceeds throughannealing after injection molding, and the resultant golf ball cover isendowed with useful properties. As used herein, the term “annealing”refers to aging through heating at a certain temperature for apredetermined period of time, or aging at room temperature for apredetermined period of time.

[0050] The surface hardness of the cover material of the golf ball ofthe present invention is preferably 40 to 80, more preferably 43 to 60,much more preferably 45 to 55, as measured by use of a D-type durometerin accordance with JIS-K6253. When the surface hardness of thecover-forming material is excessively low, the resultant golf ball tendsto produce excessive back-spin upon being hit with an iron; i.e.,controllability of the golf ball is impaired. In contrast, when thesurface hardness of the cover-forming material is excessively high, theresultant golf ball tends to produce insufficient back-spin upon beinghit with an iron; i.e., controllability of the golf ball is lowered, andfeeling on impact is impaired.

[0051] The restitution elastic modulus of the cover material of the golfball of the present invention is preferably at least 45%, morepreferably 45 to 85%, further preferably 50 to 80%, much more preferably50 to 60%, as specified by JIS-K7311. Since the thermoplasticpolyurethane material does not exhibit high restitution, preferably, therestitution elastic modulus is strictly selected. When the restitutionelastic modulus of the cover-forming material is excessively low, thetotal distance of the golf ball is considerably lowered. In contrast,when the restitution elastic modulus of the cover-forming material isexcessively high, the initial velocity of the golf ball becomesexcessively high when being shot or putted (i.e., when controllabilityof the golf is required within the range of a total distance of 100yards or less), and the golf ball may fail to meet a golfer's demand.

[0052] No particular limitation is imposed on the core employed in thegolf ball of the present invention, and any type of cores that areusually employed can be employed. Examples of the core which may beemployed include a solid core for a two-piece ball, a solid core havinga plurality of vulcanized rubber layers, a solid core having a pluralityof resin layers, and a thread-wound core having a thread rubber layer.No particular limitation is imposed on the outer diameter, weight,hardness, and material of the core. The thickness of the golf ball coverof the present invention preferably falls within a range of 0.1 to 5.0mm. The cover may have a multi-layer structure, so long as the overallthickness of the cover falls within the above range.

[0053] The golf ball of the present invention is formed so as to have adiameter and a weight as specified under the Rules of Golf approved byR&A. Typically, the diameter is at least 42.67 mm, and the weight is45.93 g or less. The diameter is preferably 42.67 to 42.9 mm. Thedeformation amount of the golf ball under application of a load of 980 N(100 kg) is preferably 2.0 to 4.0 mm, more preferably 2.2 to 3.8 mm.

EXAMPLES

[0054] The present invention will next be described in detail by way ofExamples, which should not be construed as limiting the inventionthereto.

Examples and Comparative Examples

[0055] Core composition Polybutadiene rubber 100 parts by weight Zincacrylate 21.5 parts by weight Zinc oxide 12 parts by weight Dicumylperoxide 1 part by weight

[0056] The components of the aforementioned core composition werekneaded, and then subjected to vulcanization and forming at 155° C. for20 minutes, to thereby obtain a solid core for a two-piece solid golfball (diameter: 38.5 mm). BR01 product of Japan Synthetic Rubber Co.,Ltd.) was employed as the polybutadiene rubber. The specific gravity ofthe thus-obtained core was 1.07; the deformation amount underapplication of a load of 980 N (100 kg) was 3.4 mm; and the initialvelocity as measured by means of a method specified by USGA (R&A) was78.1 m/s.

[0057] Cover materials shown in Tables 1 and 2 (unit: part(s) by weight)were kneaded by use of a twin-screw extruder at 190° C., to therebyobtain cover-forming materials. Components shown in Tables 1 and 2 aredescribed below.

[0058] Polyurethane 1 (Thermoplastic Polyurethane Material)

[0059] Pandex T8290: MDI-PTMG-type thermoplastic polyurethane material(product of DIC Bayer Polymer Ltd.) (JIS A surface hardness: 93,restitution elastic modulus: 52%)

[0060] Polyurethane 2 (Thermoplastic Polyurethane Material)

[0061] Pandex T8295: MDI-PTMG-type thermoplastic polyurethane material(product of DIC Bayer Polymer Ltd.) (JIS A surface hardness: 97,restitution elastic modulus: 44%)

[0062] Polyurethane 3 (Thermoplastic Polyurethane Material)

[0063] Pandex T8260: MDI-PTMG-type thermoplastic polyurethane material(product of DIC Bayer Polymer Ltd.) (Surface hardness as measured by useof a D-type durometer: 56, restitution elastic modulus: 45%)

[0064] Polyurethane 4 (Thermoplastic Polyurethane Material)

[0065] Pandex T7298: Non-yellowing-type thermoplastic polyurethanematerial containing aliphatic isocyanate (product of DIC Bayer PolymerLtd.) (JIS A surface hardness: 98, restitution elastic modulus: 54%)

[0066] Hydrogenated MDI

[0067] Desmodule W: Dicyclohexylmethane-4,4′-diisocyanate (hydrogenatedMDI)(product of ACI Japan Ltd.)

[0068] Isocyanate 1 (Isocyanate Mixture)

[0069] Crossnate EM30: Isocyanate master batch (product of DainichiseikaColor & Chemicals Mfg. Co., Ltd.) containing 30% 4,4′-diphenylmethanediisocyanate (isocyanate concentration as measured through amine backtitration according to JIS-K1556: 5-10%, master batch base resin:polyester elastomer)

[0070] Isocyanate 2 (Isocyanate Compound)

[0071] Desmodur TT: Tolylene diisocyanate (TDI) dimer (product ofSumitomo Bayer Co., Ltd.) (effective NCO content: 24 to 24.6 weight %,isocyanate: TDI)

[0072] Subsequently, each of the aforementioned solid cores was placedin a mold for injection molding, and a cover (thickness: 2.1 mm) wasformed from each of the cover materials—obtained by dry-mixing thecomponents (A) and (B))—around the core by means of injection molding,to thereby produce a two-piece solid golf ball (Examples and ComparativeExamples). The resultant golf ball was allowed to stand at roomtemperature for one week, and then properties of the golf ball wereevaluated. The evaluation methods are described below. A sheet(thickness: 2 mm) formed through injection molding was allowed to standat room temperature for one week, and then subjected to measurement ofcover properties. Furthermore, recyclability (i.e., formability) of thecover material was evaluated. The results are shown in Tables 1 and 2.

[0073] (Cover Properties)

[0074] Surface Hardness

[0075] The surface hardness of the cover was measured by use of a D-typedurometer in accordance with JIS-K6253.

[0076] Restitution Elastic Modulus

[0077] The restitution elastic modulus of the cover was measured inaccordance with JIS-K7311.

[0078] (Ball Properties)

[0079] Hardness

[0080] The deformation amount of the golf ball under application of aload of 980 N (100 kg) was measured.

[0081] Initial Velocity

[0082] The initial velocity of the golf ball was measured by means of amethod specified by USGA (R&A).

[0083] Total Distance

[0084] The golf ball was hit at a head speed of 45 m/s by use of No. 1wood (a driver) mounted on a swing robot machine, to thereby measure atotal distance.

[0085] Scuff Resistance Upon Being Hit with an Iron

[0086] The golf ball was maintained at 23° C., 13° C., or 0° C., andthen hit at a head speed of 33 m/s by use of a pitching wedge mounted ona swing robot machine. Thereafter, the scuff resistance of the resultantgolf ball was visually evaluated on the basis of the following criteria.

[0087] 5: No scuffing or substantially no scuffing is observed.

[0088] 4: Scuffing is observed, but is negligible.

[0089] 3: The surface of the ball is slightly scaly.

[0090] 2: The surface of the ball is scaly, and a portion betweendimples of the cover is lost to some extent.

[0091] 1: A portion between dimples of the cover is completelyexfoliated.

[0092] Yellowing (ΔYI)

[0093] A golf ball discoloration promoting test apparatus FM-1 (productof Suga Test Instruments Co., Ltd.) and a mercury lamp H400-F for colorfading test (product of Toshiba) were employed. Each of the golf ballswas irradiated with light from the mercury lamp for 24 hours. ΔYI valuesbefore and after the irradiation treatment were measured through thereflection method specified in JIS-K7103 by use of a multi-light-sourcespectrophotometer MSC-IS-2DH (product of Suga Test Instruments Co.,Ltd.). The greater the value of ΔYI, the higher the degree of yellowing.

[0094] (Formability)

[0095] Recyclability of Cover Material

[0096] A runner resin generated during injection molding was pulverizedand recycled, and recyclability of the cover material was evaluated onthe basis of the following criteria. The term “runner resin” refers to aresin formed in a runner provided for uniformly feeding a molten resinto an injection molding machine. Typically, when a thermoplastic resinproduct is formed, a runner resin is pulverized and recycled by mixingwith a virgin resin.

[0097] Possible: When a pulverized runner resin (up to 50%) was mixedwith a virgin resin, and the resultant mixture was formed into a product(i.e., a golf ball cover), problems such as offset of a core did notarise.

[0098] Impossible: Since gelation of a runner resin occurred, and therunner resin was not melted under application of heat, the resin couldnot be recycled. TABLE 1 Cover material Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5(C) (A) (a-1) Polyurethane 1 50 Polyurethane 2 50 100 100 100Polyurethane 3 100 (a-2) Hydrogenated MDI 1.5 1.5 3 1.5 1.5 Titaniumoxide 3 3 3 3 3 Polyethylene wax 1 1 1 1 1 (B) Isocyanate 1 10 10 10 1510 Cover Surface hardness 46 49 49 52 58 properties Restitution elasticmodulus (%) 50 46 46 48 48 Ball properties Outer diameter (mm) 42.7 42.742.7 42.7 42 7 Weight (g) 45.2 45.2 45.2 45.3 45.3 Hardness (mm) 3.2 3.13.1 2.9 2.6 Initial velocity (m/s) 77.1 77 77 77.2 77.3 Total distance(m) 226 227 227 227 228 Scuff resistance at 23° C. 5 5 5 5 5 at 13° C. 55 5 5 5 at 0° C. 5 5 5 5 4 ΔYI 3.5 3.5 3.5 3.5 3.5 FormabilityRecyclability Possible Possible Possible Possible Possible

[0099] TABLE 2 Comp. Comp. Comp. Comp. Comp. Cover material Ex. 1 Ex. 2Ex. 3 Ex. 4 Ex. 5 (C) (A) (a-1) Polyurethane 1 50 Polyurethane 2 50 100100 Polyurethane 3 100 Polyurethane 4 100 Titanium oxide 3 3 3 3 3Polyethylene wax 1 1 1 1 1 (B) Isocyanate 1 20 20 20 Isocyanate 2 1.5Cover Surface hardness 47 53 58 47 51 properties Restitution elasticmodulus (%) 50 48 48 45 48 Ball properties Outer diameter (mm) 42.7 42.742.7 42.7 42 7 Weight (g) 45.2 45.3 45.3 45.1 45.2 Hardness (mm) 3.3 2.82.6 3.2 3 Initial velocity (m/s) 77.1 77.2 77.3 76.7 77 Total distance(m) 226 227 228 224 226 Scuff resistance at 23° C. 5 5 5 3 4 at 13° C. 55 5 2 3 at 0° C. 4 4 4 1 2 ΔYI 6.5 6.5 6.5 3 5 Formability RecyclabilityPossible Possible Possible Possible Impossible

[0100] As is clear from Tables 1 and 2, the golf balls of the Examplesexhibit high restitution and excellent flight performance. The resultsshow that the golf balls of the Examples exhibit excellent scuffresistance upon being hit with an iron and excellent discolorationresistance. In contrast, each of the golf balls of the ComparativeExamples—in which the cover was not produced from the cover material ofthe present invention—exhibits poor restitution, and is not satisfactoryin terms of scuff resistance upon being hit with an iron and ofdiscoloration resistance. The golf ball of Comparative Example 5exhibits relatively good ball properties. However, since the reactivityof the cover material after forming is excessively high, and gelation ofthe material occurs; i.e., the material is no longer melted underapplication of heat, a runner resin generated during forming cannot berecycled.

[0101] As described above, according to the present invention, there canbe produced a golf ball having a cover which can be recycled for moldingand exhibits high restitution and excellent scuff resistance anddiscoloration resistance.

What is claimed is:
 1. A golf ball comprising a core and a covertherefor, wherein the cover is formed from a composition (C) containing,as predominant components, the following components (A) and (B): (A) apolyurethane material mixture of a thermoplastic polyurethane material(a-1) and dicyclohexyl-4,4′-methane diisocyanate (a-2), and (B) anisocyanate mixture in which an isocyanate compound (b-1) having at leasttwo isocyanate groups serving as functional groups in the molecule isdispersed in a thermoplastic resin (b-2) which is substantiallynon-reactive with the isocyanate groups.
 2. A golf ball according toclaim 1, wherein the thermoplastic polyurethane material (a-1) issynthesized from a polyether polyol and an aromatic diisocyanate.
 3. Agolf ball according to claim 2, wherein the polyether polyol is apolytetramethylene glycol having an average molecular weight of at least2,000.
 4. A golf ball according to claim 2, wherein the aromaticdiisocyanate is 4,4′-diphenylmethane diisocyanate.
 5. A golf ballaccording to claim 1, wherein, in the polyurethane material mixture (A),the ratio by weight of the thermoplastic polyurethane material (a-1) todicyclohexyl-4,4′-methane diisocyanate (a-2) is 100:0.5 to 100:5.
 6. Agolf ball according to claim 1, wherein the isocyanate compound (b-1) inthe isocyanate mixture (B) is 4,4′-diphenylmethane diisocyanate.
 7. Agolf ball according to claim 1, wherein the thermoplastic resin (b-2) inthe isocyanate mixture (B) is a thermoplastic polyester resin.
 8. A golfball according to claim 1, wherein in the isocyanate mixture (B), theratio by weight of the thermoplastic resin (b-2) to the isocyanatecompound (b-1) is 100:5 to 100:100.
 9. A golf ball according to claim 1,wherein, in the composition (C), the ratio by weight of thethermoplastic polyurethane material (A) to the isocyanate mixture (B) is100:1 to 100:40.
 10. A golf ball according to claim 1, wherein thematerial of the cover has a surface hardness of 40 to 80 as measured byuse of a D-type durometer, and a restitution elastic modulus of at least45%.
 11. A golf ball according to claim 1, wherein the material of thecover can be recycled for molding.